Apparatus for coating fasteners

ABSTRACT

A method and apparatus for coating a fastener with head and shank portions is disclosed. The invention includes the steps of and apparatus for transferring the fasteners from a feed mechanism such that the fasteners are positioned for coating. The fasteners are then conveyed through a plurality of operating stations, beginning with a heating station where the shank portions of the fasteners are heated. Subsequently, at a material applying station, a coating material is applied to the heated shank portions. A preferred embodiment of the method and apparatus of the present invention includes using a magnetic holder to carry the fasteners horizontally by their head portions, where fasteners are centered by a rotating wheel, heating the shank portion to a temperature above the melting point of the applied material and applying the material to the heated shank portion to form a coating thereon. The magnetic holders are part of an endless traveling belt that rotates continually. The fastener carriers have teeth that engage a rack to rotate the fasteners. A conveyor provides added air cooling for the coated fasteners, which can continue to be rotated. Also disclosed is a transfer wheel with two sets of notches that is synchronously coupled to the traveling belt for placing and aligning fasteners on the belt for coating. Uncoated areas on the fasteners may be detected via sensors present beyond the powder spray station which may include a plurality of spray nozzles.

This application is a continuation-in-part of prior U.S. Ser. No. 07/748,773, filed on Aug. 22, 1991, now U.S. Pat. No. 5,169,621 which is a divisional of U.S. Ser. No. 07/422,602, filed on Oct. 17, 1989 issued as U.S. Pat. No. 5,078,083 on Jan. 7, 1992.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an apparatus and method for coating fasteners, and more particularly to an improved method and apparatus for coating fasteners with shank and head portions.

BACKGROUND OF THE INVENTION

Numerous methods and devices have been employed in the past for coating fasteners. Some of these methods and devices are useful in coating certain types of fasteners, but are not as versatile in coating other types of fasteners.

Examples of such methods and devices include U.S. Pat. No. 3,452,714 in the names of G.F.C. Burke, Richard J. Duffy et al.; U.S. Pat. No. 4,120,993 to Richard J. Duffy et al.; and U.S. Pat. No. RE 28,812 to Richard J. Duffy, one of the present inventors. The methods and devices disclosed in these United States Patents provide for the coating of fasteners in which the shank portion of the fastener depends below a pair of traveling belts. These fasteners are supported on the belts at their head portion. The methods and apparatus of the previously described patents do not provide the ability to precisely control the linear speed and rotation of the fasteners during the coating process. Also, it would be advantageous to provide a method and apparatus which would automatically and rapidly coat a wide variety of different fastener configurations and which may be adapted for use with a variety of different types of coatings.

It would also be advantageous to provide a method and apparatus which accommodates a variety of different fastener configurations and sizes and which could be quickly and easily adapted for coating such fasteners. In addition, it is desirable to provide a method and apparatus which has the versatility to coat a specified portion of the threads of the fastener, as well as the complete threaded area, and further, a method and apparatus which may coat only a specific portion of the radial distances about the threaded surface of the fastener. Furthermore, it would be advantageous to provide a method and apparatus which provides the ability to precisely control the linear speed and rotation of the fasteners to be processed.

The solutions to some of these problems have been disclosed in the application, Ser. No. 070,416, filed Jul. 7, 1987, claims of which have been allowed and the disclosure of which is incorporated herein by reference. Improvements, however, are still desirable to increase the speed and efficiency of the apparatus and method, allow for faster and easier adaptation to fasteners of different configurations and sizes, create a smoother and more even coating of material, allow the use of different types of coating, and prevent clogging of the coating nozzle.

SUMMARY OF THE INVENTION

The present invention is an apparatus that applies a coating to fasteners. Prior to having the coating applied by the appropriate means, the fasteners are passed through a heating means such as an induction coil. The fasteners travel through the heating means and by the coating means on an advancing means such as a traveling belt. Fasteners are directed onto the advancing means by a transferring means such as a transfer wheel, that receives aligned fasteners in a continuous supply.

In a preferred embodiment the traveling belt has equally spaced, removable, magnetic carrying members that hold the fastener heads. A fastener or stud centering wheel or moving belt centering device may be employed to ensure that the fasteners are centered on their respective magnetic holders. Alternatively, two centering wheels may be used to center the fasteners. Such mechanical centering of the fasteners on their magnetic holders obviates the need for hand centering to avoid arcing out of the induction coil when the non-centered fastener passes therethrough. An evenly applied coating to the fastener is assured by a means for controlling the degree of surface coating on the fasteners, which can be, among other arrangements, a rack of teeth engageable with complementary teeth on the carrying members to provide for their rotation. Full rotation of the fasteners ensures an even, typically 360 degree coating of material, while a less than full rotation can limit the application of the coating to less than 360 degrees if the Coating is only applied from one direction. Rotation of the fasteners after the application of the coating is complete improves the smoothness and evenness of the coating, especially with liquid coatings. Such additional rotation also facilitates cooling. A coating inspection station may be added which includes preferably optical sensors to detect any uncoated areas on the fasteners. The sensors can generate a signal to the user to indicate unsatisfactory coating.

Another preferred feature of the invention is the transfer wheel or carrier that places the fastener on the traveling belt. The wheel has two sets of notches, one that carries the fasteners and another that interacts with a biased striking element to move the fasteners from the wheel to carrying members on the belt. The transfer wheel and the belt are driven by the same motor and pulley system, so that the wheel is easily adjusted to accommodate different configurations and sizes of fasteners.

In another preferred embodiment, the fasteners are moved from the traveling belt to a cooling conveyor. The conveyor belt is preferably an air permeable mesh, so that air curtains or air knives can be placed around the conveyor to more quickly cool the coated fastener.

Another desirable feature of the apparatus of the present invention is a spray nozzle that is particularly effective with powder coatings. An interior surface disburses the material, whose velocity is increased by a secondary source of air supplied at the top of the nozzle. Flattening the outlet of the nozzle provides additional control to the applicability of the coating, as does making the nozzle rotatably adjustable to accommodate various coating lengths. In an alternative embodiment, a plurality of spray nozzles may employed to provide more uniform coating with an increased production rate.

Other features include a cover made of materials sold under the trademark TEFLON® polytetrafluoroethylene for the magnetic carrying member to protect the magnet end from becoming coated when coating is applied to the entire fastener. The magnetic insert of the carrying member can also be made to be removable.

A process using the described features is also provided.

DESCRIPTION OF THE DRAWINGS

The novel features which are characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and attendant advantages thereof, will be best understood by reference to the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic of the process and device practicing the present invention;

FIG. 2 is a perspective view of an apparatus practicing the present invention;

FIG. 3 is a perspective view of portions of the aligning means, transfer wheel and traveling belt of the apparatus of FIG. 1;

FIG. 4 is a perspective view of the geared ends of the carrying members of the apparatus of FIG. 1 as they engage the rack of teeth for rotation;

FIG. 5 is a perspective view of the transfer wheel of the apparatus of FIG. 1 with the striking member biased away from a fastener and the traveling belt;

FIG. 6 is a perspective view of the striking member of the apparatus of FIG. 1 after it has been biased into one of the second set of notches to transfer the fastener to the traveling belt;

FIG. 7 is an exploded view of an applicator nozzle with a flattened outlet shown in phantom;

FIG. 8 is a perspective view of an alternative embodiment of an apparatus practicing the present invention;

FIG. 9 is a side view of a rotating stud centering wheel of the present invention; and

FIG. 10 is a side view of a moving belt stud centering device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic drawing that outlines the general features of the method and apparatus of the present invention. A general description will be followed by a more specific one. A continuous supply of fasteners is provided as fasteners are transferred from a bulk storage device 12 to a conventional bucket elevator and a conveyor 14, which dumps the fasteners into a vibrating distribution and orientation device 16, such as one commercially available from Moorfeed Corp.. The fasteners emerge from the vibratory bowl onto a dispensing track 18, at which time the heads and shanks of all fasteners are aligned in the same direction. Preferably the shanks are parallel to the floor.

The fasteners then slide into notches 22 (FIG. 5 and 6) spaced equally around the perimeter of a transfer wheel or carrier 20. Transfer wheel 20 is driven by a 5 horsepower DC motor that, by way of belts and pulleys, also drives a traveling belt means such as a traveling belt 50. A striking assembly (shown in FIGS. 5 and 6) displaces the fasteners onto magnetized carrying members 52 (FIG. 2) of the traveling belt. The fasteners are passed through a heating station such as an induction coil 65 to heat the surface of the fastener to a temperature at which the coating to be applied will adhere. In the case of powder sold under the trademark TEFLON® approximately 700°-900° Fahrenheit is the preferred temperature range. Still more preferable is approximately 775°-825° Fahrenheit. This can be achieved by a variety of methods. One such method is induction heating, utilizing a 75 kilowatts -10k Hz power supply and an appropriate induction coil. This low frequency provides deeper current penetration for heating of the fastener at reduced costs. The power to the coil can, of course, be varied by the appropriate controls known to those in the art. As one skilled in the art may appreciate, a variety of power supplies with various power ratings and operating frequencies can be used, depending on the type and size of fasteners to be processed.

After the fasteners pass through the induction coil, a rack of teeth 102 engages and begins to rotate the fasteners, which then pass under a device that dispenses the material used for forming the coating on the fasteners. Powdered materials for forming such coatings are supplied in a manner described in part in the previously incorporated references, specifically through a dispensing nozzle 70 onto the fasteners. Excess powder is salvaged by a vacuum pick-up 72 on the other side of nozzle 70. To ensure an even coating, the fasteners can be further turned subsequent to the application process. Depending upon the necessary parameters of the coating process, the rack of teeth can be used to rotate the fasteners at any position in the heating, coating, and/or cooling steps of the process.

A cooling conveyor 120 is provided to further cool the fasteners before they are immersed in a final bath for cooling and/or the application of a rust inhibitor. The conveyor 120 can be operated in ambient conditions, or it can be used in association with devices such as air amplifiers or air knives 125. Additional cooling may be utilized to lower the temperature of the fasteners below the boiling point of the final bath. In addition, when a coating sold under the trademark TEFLON® is used, gradual cooling is preferred to allow the coating sold under the trademark TEFLON® time to set. Otherwise rapid cooling may reduce the quality of the bond between the fastener and the coating, resulting in a lower level of adhesion.

FIG. 2 depicts in detail many of the aspects of the present invention. A portion of the means for providing a continuous and aligned supply of fasteners is shown generally as 10, and incorporated in the apparatus of FIG. 1 including bulk storage device 12, bucket elevator and conveyor 14, vibrating bowl 16, and dispensing track 18. These are all commercially available and known to those of ordinary skill in the art.

As the fasteners 11 come off the dispensing track 18, they are aligned preferably so that the shanks are horizontal and the heads are vertical. The shanks slide into a first set of notches 22 on transfer wheel 20. Transfer wheel 20 can be directly turned by an output shaft connected to a direct current (D.C.) motor (not shown, see U.S. Patent application Ser. No. 070,416) or by a belt 24 and pulleys 26 and 27. If the motor is not connected directly to transfer wheel 20, then it drives sprocket 32 which turns traveling belt 50. By means of the belts and pulleys, preferably, one motor synchronously turns the transfer wheel 20 and traveling belt 50. In this way, the traveling belt and the transfer wheel can preferably be adjusted into alignment quickly to accommodate a variety of fastener sizes.

The principal features of the structure and operation of the transfer wheel 20 are depicted in FIGS. 3, 5, and 6. As noted earlier, a head 29 of striking element 28 contacts fastener 11 at the moment the fastener is aligned with a magnetic carrying member 52. The fastener 11 is then held by the magnetic force of carrying member 52 as the fastener is lifted out of the notch by the motion of the belt 50 and associated carrying member 52.

Particularly as shown in FIGS. 5 and 6, wheel 20 also has a second set of notches 34 on the side of the wheel which preferably cooperate with striking element 28 biased by spring 36. The notches 34 are preferably trapezoidal in shape, with striking element 28 biased to move into the notch. As the wheel or carriage rotates in the direction of Arrow A, angled side 34B works against the biasing force (Arrow B) exerted by spring 36 to move striking element 28 upwardly from lower notch surface 34C to flat upper notch surface 34E. As the wheel continues to rotate, surface 34E slides against striking element 28 until the edge of the striking element completely clears the upper surface 34E and the edge of vertical side 34D. Spring 36 then pushes element 28 completely into the next notch. Head 29 of striking element 28 then engages fastener 11 moving it into contact with magnetic carrying member 52.

In the event that a fastener 11 is not centered on magnetic carrying member 52, a fastener centering device is provided. As shown in FIGS. 8 and 9, a fastener centering device 210 centers fastener 11 on its magnetic holder 52 so that its longitudinal axis is substantially aligned with the longitudinal axis of the corresponding magnetic holder 52.

Turning now to FIG. 8, 9, and 10, various embodiments of the centering device of the present invention is shown. In FIG. 9, a single wheel 212 centering device is positioned half the fastener head diameter from the center line of the magnet holder 52. The centering wheel is preferably made of aluminum but could be stainless steel or of a non-magnetic material. The centering wheel 212 rotates in a clockwise direction while the fasteners 11 rotate in a counter-clockwise direction when the fastener travel direction is from right to left as shown in FIGS. 8 and 9.

Wheel 212 is mounted to a motor (not shown) via shaft 214. The wheel 212 is positioned in the same plane as the heads of fasteners 11 so that the centering force is applied as close to the face of the magnet holder 52 as possible. The surface speed of the wheel and the fastener are equal to eliminate drag forces between them.

In operation, as shown in FIG. 9, a fastener 11 in position A that is not properly centered on magnet holder 52, moves left toward centering wheel 212. In position B, the fastener 11 remains uncentered. At position C, fastener 11 contacts the edge of centering wheel 212 and is thereby forced to the center of the magnet holder 52. Once beyond the contact point with the centering wheel 212 at point D, the fastener should be properly centered on magnetic holder 52. All centering occurs on the lead-in half of the wheel 212. If the fastener 11 is not centered by the time it passes the wheel vertical center line at point D, that misalignment will remain.

To further improve centering and to prevent the aforementioned misalignment, two centering wheels can be positioned above and below the path of the fasteners. Two wheels, appropriately spaced a vertical center line would also provide centering with added accuracy.

As shown in FIG. 10, a moving belt arrangement may also be employed to center the fasteners 11 on their respective magnetic holders 52. A moving belt 316 about wheels 310 and 312 is provided and mounted in similar fashion to the single centering wheel 212 shown in FIG. 8. A belt support 314 supports belt 316 while fasteners pass over to ensure that the magnet holders are on a constant center line with respect to the belt. In similar fashion to the single wheel centering device of FIG. 9, the moving belt serves also to align the fasteners as they rotate and move linearly. By providing a sufficient belt length that is longer than the circumference of the largest sized fastener head, the aforementioned problem with remaining misalignment can be eliminated. Accurate and consistent centering, which can be aligned through a single or double wheel or a supported belt, that can be realized with the present invention, avoids contact of the fasteners 11 with induction coil 65 which would result in arcing out of the induction coil 65. Further, this mechanical and automatic centering obviates the need for hand centering which is tedious and reduces the production rate of the apparatus. Further, due to this more accurate centering, the gap between the induction coil 65 and the fasteners may be reduced and subsequently adjusted for each fastener size to obtain a significant increase in heating rate. The gap between the induction coil 65 and the fasteners 11 passing therethrough may be adjusted to the specific fastener size. Since the field strength of the induction coil 65 decreases with the cube of the distance from the inductor, a significant increase in the heating rate and production rate with more uniform coating can be achieved.

Traveling belt 50 is preferably an endless chain of links 54 that is driven by sprocket 32 and supported by a second sprocket 33 (FIG. 2). Although other types of carrying assemblies such as belts, wire, cords and the like can also be used. Various structures, such as connectors 56, can be used to connect carrying members 52 to chain links 54 (FIG. 4). The carrying members 52 are preferably hollow, so that permanent magnets 60 can be inserted and held in place by set screw 62, thus forming a magnetic holding means (FIGS. 5 and 6). This configuration has the advantage of securing the fastener in correct position for coating. The carrying members are preferably aluminum shells, while the inserts are preferably ALNICO V heat resistant permanent magnetic assemblies.

Fasteners 11 are moved through a heating station, such as induction coil 65, and then under a means for applying the coating material, such as nozzle 70. A means for removing excess coating material, such as vacuum pick-up 72, is associated with the application nozzle. A drip pan or other drainage device can be used if the coating material is a liquid. The coating material, preferably a powder material, is applied from a source (not shown) that preferably fluidizes the powder and conveys it under pressure to the nozzle 70. Other embodiments, however, are also contemplated where a powder coating material may be provided by a vibratory gravity feed device, or a liquid coating material is provided under pressure or gravity, depending upon the physical characteristics of the material. Electromechanical and hydraulic control of the coating application, belt speed, heating element, and other devices with variable characteristics can be exercised by various means known to those of skill in the art.

More specifically, an alternative means for applying the coating material is shown in FIG. 8. This embodiment of the present invention includes a number of spray nozzles each with a separate stream of material preferably from the same powder source. As shown in FIG. 8, spray nozzle 80 is provided in addition to spray nozzle 70. The addition of a second spray nozzle enables the apparatus to achieve a more uniform coating of material. This second nozzle ensures a uniform 360 degree coating about a fastener particularly where the fastener is relatively long which might not get adequate coverage of material. As a result of superior coating performance, an increase in production rate can be realized.

As shown in FIG. 4, carrying members 52 are rotated by an assembly 100 for controlling the degree of surface coating on the fasteners. Assembly 100, as included in the apparatus of FIG. 1, may include a rack of teeth 102 engageable with rotating pinions 104 on the ends of rotating carrying members 52. The first portion 106 of rack 102 (with reference to the motion of belt 50, as signified by Arrow B) is separate from the remainder of rack 102 and pivotable about spindle 108. This facilitates proper and efficient engagement of the pinions 104 with teeth 102. Without the pivoting capability, the teeth of the two engaging objects might not mesh properly. A biasing member (not shown) is located between lower plate 110 and first portion 106 to create a biasing force as shown by Arrow C. Any one of a number of different types of springs, attached to spindle 108 or under first portion 106, can provide the necessary force.

Typically controlling means 100 will rotate the fasteners through 360° during the application of the coating material, although specific lengths of rack 102 can result in rotations more or less than 360° to provide coating of selected circumferential portions of each fastener 11. When rack 102 is removed, the fasteners typically are coated on "one side," i.e., 180° degrees of the shank. Rack 102 can be extended in either or both directions from the coating application station. The extension of rack 102 beyond the coating station enables the continuing rotation of the fastener for a period of time limited only by the length of belt 50 and teeth 102. The same technique is also effective when a liquid coating, such as the liquid coating sold by Nylok Fastener Corporation under the trademark PRECOTE® is applied. If the fasteners are sufficiently rotated, the need is eliminated to remove drops of liquid that otherwise form on the bottom of the fastener. Such removal would typically be performed by a stationary brush located adjacent to the belt.

Prior to removal of the fasteners from their respective magnetic holders, detection of proper coating may be accomplished through the employment of a coating inspection station as shown in FIG. 8. Sensor 90 may be positioned on the apparatus at a point beyond or after the powder spray station with spray nozzle 70 which may also include second spray nozzle 80. Sensor 90, which is preferably an optical sensor, may be mounted to a bracket (not shown) to secure it in place in close proximity to the path of fasteners 11. A plurality of sensors 90 may be used for further and more accurate detection of the material coating on the fasteners. The sensors determine whether the coating that has been applied meets a predetermined coating specification. Typically, this coating specification is the presence of coating on the fastener. Cable 92 transmits information detected by sensor 90 when the coating has not met its specification, for example, where coating has not been applied to the full 360 degrees about the fastener. This information is preferably a signal to the user to indicate the fasteners are not being properly coated.

When rotation of the fastener is no longer necessary, the belt 50 can be moved by stationary discharge cam 115, which contacts the heads of each passing fastener 11 and causes each fastener to slide off the end of magnet 60, down slide 117, and onto cooling conveyor 120. Cooling conveyor 120 preferably includes a mesh belt 122 that permits the easy movement of air around fastener 11. Ambient air can be used to further cool the fastener, or forced air can provide additional cooling. As shown schematically in FIG. 1, air amplifiers or air knives 125 can blow forced air in and around the fasteners for still additional cooling.

The final step of the coating process should include the immersion of the fasteners in a liquid bath material 128, as contained in receptacle 130. The bath material 128 can be water, oil, or another chemical agent. The bath is designed to cool the fastener to a temperature relatively close to ambient, and can also provide a coating of rust inhibitor on the fastener.

Finally, the fasteners are moved out of the bath by conveyor 135 and move to another location for storage or packing.

FIG. 7 depicts an exploded view of the preferred embodiment of the nozzle 70 used to spray powdered material such as powder sold under the trademark TEFLON® on the fasteners. The preferred nozzle includes a cylindrical body portion 172 with a conical end 174. The tip of the nozzle 170 can be a small outlet 176, or a broader, flatter one as shown in phantom as 178. Inside body portion 172 is a torpedo 180 for dispersing powder. Torpedo 180 is located toward the opening end of body 172. After the powder has entered the nozzle at top 184, it moves through passageway 187, and then encounters a smaller, cone which is surrounded by annular element 180A projecting from torpedo 180. Cone 182A of cone torpedo 182 thus initially disperses the powder after it has entered the nozzle at top 184 into three slots 186 (only two of which are shown) spaced radially around cone torpedo 182. To accelerate the powder and prevent clogging of the outlet, a secondary source of air is provided through hose 190 into manifold 192. Preferably, the secondary air source should be pressurized above the pressure level of the incoming powder that is transported by a primary air source. This secondary air source assists in providing a steady and even flow of powder to and at the output of nozzle 170. This preferred configuration substantially eliminates any flutter in the powder output and provides an improved, uninterrupted supply of powder which assures an improved coating on each fastener.

The secondary air is fed from manifold 192 sealed by O-rings 193, through passageway 194, out apertures 196, and into the interior chamber defined by the outside of body portion 172 and conical end 174. The configuration of the apertures can be embodied several ways. One embodiment includes apertures 196 spaced approximately 30 degrees on either side of each slot 186. Other forms could include a series of 12 equally spaced apertures 196 or a cylindrical manifold extending laterally the complete circumference of nozzle 170 and vertically from manifold 192 to aperture 196 as now depicted in FIG. 7.

Another desirable feature is to make the nozzle 70 rotatable about an axis extending from its outlet to its top. Thus, when the nozzle end is configured as shown by the flattened outlet 178, the length of the shank portion of the fastener that receives a coating of material can be controlled. The capability to rotate nozzle 70 approximately 180 degrees is preferred. Vacuum pick-up 72 could be adapted to rotate with nozzle 70, or, alternatively, could be made large enough to eliminate the need for rotation.

The present invention can also be used with liquid coatings, such as such as the liquid coatings sold by the Nylok Fastener Corporation under the trademark PRECOTE®. The fastener is initially heated by an induction coil to approximately 150° Fahrenheit, coated, and rotated to obtain a uniform 360 degrees coating on the fastener. Heat is applied after the application process to dry the coating. Subsequent post coating operations are designed to remove the carrier solvent or dispersing medium from the coating.

The method and apparatus of the present invention can be adapted for a wide variety of liquid coating applications. Either gravity or pressure can be used in applying the coating. Moreover, a broad range of viscosities of the liquid coating can be accommodated, including water or solvent based dispersions and/or solutions. These include coatings such as a toluene-based coating sold under the trademark PRECOTE® 80 or a water-based coating sold under the trademark PRECOTE®.

If it becomes desirable to coat the sides of the head of the fastener, thin caps can be used to cover the otherwise exposed magnet to prevent accumulation of the coating on the magnet 60 and carrying member 52. Such caps can be made of a material such as those sold under the trademark TEFLON® or any other suitable material. In the same manner as the caps, a longer adaptive element can slide over a longer part of carrying member 52. The adaptive element can have a saddle or clip end, such as clip 75 shown in FIG. 5, that will mechanically hold the head of a non-ferromagnetic fastener or stud.

Of course, it should be understood that various changes and modifications to the preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is, therefore, intended that such changes and modifications be covered by the following claims: 

What is claimed is:
 1. An apparatus for continuously applying a coating material to fasteners, comprising:means for providing a supply of fasteners; means for positioning the fasteners on fastener supporting notches on a rotating carriage. means for transferring the fasteners from said rotating carriage to a belt with externally threaded fastener holders that are synchronously alignable with said supporting notches; means for moving said belt to advance the fasteners positioned on said fastener holders; means for centering the fasteners positioned on said corresponding fastener holders on said moving belt; means for heating the fasteners positioned on said externally threaded fastener holders to raise the temperature of the fasteners above the melting point of the coating material; means for advancing the fasteners through said heating means; means for applying the coating material to at least a portion of said fasteners positioned on said externally threaded fastener holders; and means for rotating said fastener holders while said coating material is applied to said fasteners.
 2. The apparatus of claim 1, wherein said means for centering is at least one rotating wheel positioned adjacent said fasteners.
 3. The apparatus of claim 1, wherein said means for centering is a moving belt positioned adjacent said fasteners.
 4. The apparatus of claim 3, wherein said moving belt has a length greater than the circumference of the head of one of the fasteners.
 5. An apparatus for continuously applying a coating material to fasteners, comprising the steps of:means for providing a supply of fasteners; means for positioning the fasteners on fastener supporting notches on a rotating carriage; means for transferring the fasteners from said rotating carriage to a belt with externally threaded fastener holders that are synchronously alignable with said supporting notches; means for moving said belt to advance the fasteners positioned on said fastener holders; means for heating the fasteners positioned on said fastener holders to raise the temperature of the fasteners above the melting point of the coating material; means for advancing the fasteners through said heating means; at least one nozzle for applying the coating material to at least a portion of said fasteners positioned on said fastener holders; and means for rotating said fastener holders while said coating material is applied to the fasteners.
 6. The apparatus of claim 5, wherein said at least one nozzle may be rotated to control the applied coating surface area on the fasteners.
 7. The apparatus of claim 5, wherein said at least one nozzle provides a uniform coating about the fasteners.
 8. An apparatus for continuously applying a coating material to fasteners, comprising the steps of:means for providing a supply of fasteners; means for positioning the fasteners on fastener supporting notches on a rotating carriage; means for transferring the fasteners from said rotating carriage to a belt with externally threaded fastener holders that are synchronously alignable with said supporting notches; means for moving said belt to advance the fasteners positioned on said fastener holders; means for heating the fasteners positioned on said fastener holders to raise the temperature of the fasteners above the melting point of the coating material; means for advancing the fasteners through said heating means; means for applying the coating material to at least a portion of said fasteners positioned on said fastener holders; means for rotating said fasteners holders while said coating material is applied to said fasteners; and means for sensing whether the applied coating meets a coating specification.
 9. The apparatus of claim 8, wherein said sensing means for is an optical sensor.
 10. The apparatus of claim 8, wherein said sensing means includes a means for signaling that the coating has not met the coating specification. 